The present invention relates to a valve timing control device for use in an internal combustion engine for continuously controlling or varying the timing at which an intake or exhaust valve is opened and closed.
One known valve timing control device for use in internal combustion engines is disclosed in Japanese Laid-Open Patent Publication No. 61-268810, for example.
The disclosed valve timing control device includes a phase adjusting mechanism for varying the relative phase or angular relationship between a timing pulley and a camshaft to control or vary the timing at which an intake or exhaust valve is opened and closed. The phase adjusting mechanism has a piston movable between two positions. The piston reaches one of the positions when hydraulic pressure is supplied to a hydraulic pressure chamber and reaches the other position when hydraulic pressure is released from the hydraulic pressure chamber. The timing at which the intake or exhaust valve is opened and closed is only controlled such that it is advanced or retarded a certain fixed amount.
Another problem with the earlier valve timing control device is that the timing pulley is mounted on a housing having opposite ends supported by respective rotatable shafts. Therefore, the piston has a small pressure-bearing area and is operable at a limited speed.